1. Field of the Invention
The present invention relates to a liquid application device and an inkjet recording apparatus, and particularly to a liquid application device for applying liquid to a medium for a certain purpose which is, for example, to promote the coagulation of pigment when recording is carried out using an ink which contains the pigment as a coloring material. The present invention also relates particularly to an inkjet recording apparatus which includes a mechanism for applying liquid to a recording medium used in inkjet recording, for a purpose which is, for example, to promote the coagulation of pigment when recording is carried out using an ink containing the pigment as a coloring material.
2. Description of the Related Art
Conventionally, in the field of printing, a configuration is known in which an area, where ink as application liquid is supplied to a roller, is sealed off (see Japanese Patent Application Laid-open No. 8-58069 (1996)). An application mechanism described in the above Japanese Patent Application is a mechanism applying ink to a roller of which a pattern of a printing plate is formed on the surface, in a gravure printing apparatus. In this apparatus, an ink chamber having two doctor blades is used. The two doctor blades extend in the longitudinal direction of the roller at positions corresponding to upper and lower portions along the circumferential surface of the roller. Moreover, elastic members are provided on both side portions of each of these two doctor blades. The ink chamber is brought into contact with the circumferential surface of the roller, and thereby, a liquid room is formed between the chamber and the roller.
In the gravure printing apparatus described in Japanese Patent Application Laid-open No. 8-58069 (1996), the elastic members provided on both side portions of each of the doctor blades are different members from the doctor blades. The elastic members are brought into contact with the roller in order to form the liquid room. Here, the position of the ink chamber having the doctor blades and the elastic members is fixed. Only with this, a contact pressure when the doctor blades and the elastic members are brought into contact with the roller is generated. A shaft having a thread groove is engaged with this ink chamber, and the ink chamber is moved by the rotation of the shaft. With the aforementioned configuration, the roller is rotated, and thereby the application liquid in the liquid room is supplied to the roller.
In the case of the apparatus described in Japanese Patent Application Laid-open No. 8-58069 (1996), since the roller is in contact with the elastic members, abrasion of the roller is caused as the roller rotates. The abrasion of the roller shortens the working life of the roller. Then, shortening of the roller working life leads to the shorter working life of the apparatus and an increase in frequency of exchange of rollers.
Moreover, the abrasion of the roller does not uniformly occur on the roller surface and the abrasion loss differs from portion to portion of the roller surface. To be more specific, as the number of rotations for applying liquid to application media is increased, a portion of the roller on which the application media pass, in other words, which has come in contact with the application media, are more abraded away than a portion of the roller where the application media do not pass. For this reason, only the portion of the roller which has come in contact with the application media becomes thin. Accordingly, the abrasion loss of the roller is increased at the portion of the roller where the application media frequently pass.
Since there are application media of various sizes such as A4, A5, A3, B5, B4 and so on in the market, a recording apparatus includes a roller with a width corresponding to the maximum width of the supportable application media, in order to handle various sizes of the application media. Taking an example of an apparatus where the right edge of the roller is used as a base along which the application medium is set, there is a remarkable difference in the frequency with which the application media pass between the base side and the opposite side (hereinafter called as a non-base side). In other words, in the case of the base side, any sizes of the application media pass without fail. In the case of the non-base side, however, some sizes of the application media do not pass, depending on the sizes. This results in causing a difference in the abrasion loss between the base side and the non-base side.
This is because a frictional force between the roller and the elastic members contacting with the roller is changed depending on the presence or absence of an application liquid, serving as a lubricant. That is, in this case, the frictional force varies with the portion of the roller where the application media pass and the portion thereof where the application media do not pass. Accordingly, the roller is abraded away at the portion where the application media frequently pass. As described above, the difference in the abrasion loss depending on the portions of the roller causes unevenness of application in one sheet of the application media.
Moreover, since the ink chamber is fixed while the elastic members are in contact with the roller, the contact pressure to the roller is changed when the diameter of the roller becomes smaller due to the above-mentioned abrasion. The change in contact pressure affects an application amount. Therefore, unevenness of the application amount to the application medium occurs for each application operation depending on the number of times of use of the roller.